Half of stars may be orphans with no galaxy: study

As many as half of all stars may be orphans that lie in what had been thought to be dark spaces between galaxies, according to a sounding rocket experiment conducted by US space agency NASA.

Observations from the Cosmic Infrared Background Experiment (CIBER), published Thursday in the U.S. journal Science, detected a surprising surplus of infrared light in the dark spaces between galaxies, a diffuse cosmic glow that is as bright as all known galaxies combined.

The researchers said that the best explanation is that the cosmic glow originates from stars that were stripped away from their parent galaxies and flung out into space as those galaxies collided and merged with other galaxies.

"We think stars are being scattered out into space during galaxy collisions," lead author Michael Zemcov of the California Institute of Technology (Caltech) and NASA's Jet Propulsion Laboratory (JPL) said in a statement.

"While we have previously observed cases where stars are flung from galaxies in a tidal stream, our new measurement implies this process is widespread."

Using suborbital sounding rockets, which are smaller than those that carry satellites to space and are ideal for short experiments, the CIBER research captured wide-field pictures of the cosmic infrared background at two infrared wavelengths shorter than those seen by Spitzer.

Because the atmosphere of Earth itself glows brightly at these particular wavelengths of light, the measurements can only be done from space.

During the CIBER flights, the cameras were launched into space, then snapped pictures for about seven minutes before transmitting the data back to Earth.

Scientists masked out bright stars and galaxies from the pictures and carefully ruled out any light coming from more local sources, such as our own Milky Way galaxy.

What's left is a map showing fluctuations in the remaining infrared background light, with splotches that are much bigger than individual galaxies.

The brightness of these fluctuations allows scientists to measure the total amount of background light.

To the surprise of the CIBER team, the maps revealed a dramatic excess of light beyond what comes from the galaxies.

The data showed that this infrared background light has a blue spectrum, which means it increases in brightness at shorter wavelengths

According to the researchers, this is evidence the light comes from a previously undetected population of stars between galaxies, while light from the first galaxies would give a spectrum of colors that is redder than what was seen.

"The light looks too bright and too blue to be coming from the first generation of galaxies," said James Bock, principal investigator of the CIBER project from Caltech and JPL. "The simplest explanation, which best explains the measurements, is that many stars have been ripped from their galactic birthplace, and that the stripped stars emit on average about as much light as the galaxies themselves."

The researchers collected data from two separate flights, launched from White Sands Missile Range in New Mexico in 2010 and 2012, and validated their results with NASA's Spitzer Space Telescope.